Many computer applications and operating systems use a heap-based memory-allocation scheme to manage the usage of memory resources within a computer system. For example, an application process can request a block of memory from the heap for its own use and then return control of the block of memory when the application has finished using the block. All too often, a process can cause problems with the heap by mishandling protocols associated with the heap and/or corrupting memory stored on the heap.
Heap corruptions/memory problems can take many forms including random overwrites, buffer overruns, “double frees,” and memory “leaks.” Random overwrites typically occur when a process references already freed memory or when other errors cause pointers to be misdirected. Buffer overruns typically occur when a process allocates a block of memory that is too small and writes over and beyond the end of the allocated block. Double frees occur when a process frees the same buffer twice, which leads to the possibility of the freed block of data being allocated twice. Memory leaks may occur, for example, when an application repeatedly requests more memory space (often while not efficiently using the memory space it has already allocated).
Heap corruptions are typically one of the most difficult types of bugs to locate and identify. Because of the dynamic nature of the heap, they are often difficult to reproduce and/or to document because traces of the corruption may be erased before the source of the problem is identified. Furthermore, heap corruptions may occur in systems that are being used by customers, which can complicate attempts at debugging and maintenance. What is needed is a mechanism to improve the diagnostic capabilities of system tools for maintenance and debugging heap corruptions and memory problems.